Definitions of Words used in the Articles
MUTAVI
Research & Advice Group, The Netherlands
Albinism:
- A group of inherited conditions which include a decrease in the amount of
pigment in
- the eyes, skin and feathers.
Allele:
- Just a specific variation of a gene
Autosomal:
- Referring to a chromosome other than one of the sex (Z or W) chromosomes.
Cell:
- The container for chromosomes. A Budgerigar cell carries at least 30 chromosomes in
- a gamete cell or at least 30 chromosome pairs in all other cells.
Chromosome:
- A microscopic structure, made out of DNA, which carries the genes. All cells
within
- the body have a set of chromosomes. Each chromosome contains a large number of
- genes except for the W-chromosome in female birds.
Co-Dominance:
- The lack of dominant or recessive traits allowing both alleles in a chromosome pair to
- express themselves.
Cross section:
- A cross section is a cut through something (such as a feather shaft) at an angle perpendicular to its axis in order to
- view
its interior structure.
Crossover:
- When a pair of chromosomes trade genes.
DNA:
- Desoxyribonucleic acid, a natural substance which stores genetic information as an
-
intertwined double chain. The body reads the code stored in this chain to learn how to
-
assamble proteins from amino acids.
Dominant:
- The opposite of recessive. A gene that is visible when paired with other genes. The
- most expressive gene at the allele of a chromosome pair.
DOPA:
- Dihychoxyphenylalanine, a natural chemical which the body makes as a step in the
-
process of making the pigment melanin.
Epistasis:
- The suppression of a gene by the effect of an unrelated (epistatic) gene.
Eumelanin:
- A black or brown form of the pigment melanin as is to be found in e.g. Budgerigars.
Featherbulb:
- The "root" of a bird feather, from which growth and coloration of the feather
develops.
- Featherbulbs go through moulting cycles, and when moulting or the feather is
pulled
- out, a new one starts to grow after three days.
Gene:
- A piece of information, stored in a code in DNA, which tells the body how to make a
-
particular protein.
Hemizygous:
- Hens, having only one copy of the Z-chromosome or a human male having only one copy of the Y-chromosome.
Hypopigmentation:
- A general term for decreased or total absence of pigmentation or coloration.
Hypostasis:
- The inability of a gene to produce its usual effect when coupled with another gene that is epistatic
toward it.
- Such a gene is called hypostatic.
Iris:
- The normally white colored part visible in the eyes of Budgerigars, which closes in and
-
opens out around the pupil.
Locus:
- A location on a chromosome or chromosome pair. A specific place that defines an
- allele.
Melanin:
- A type of pigment made in the eyes, skin and feathers.
Melanocyte:
- A type of cell specialized to make the pigment melanin. Melanocytes are
located in the
- skin, the featherbulbs and the eyes. Researchers have found melanocytes in the
skin,
- featherbulbs and eyes of birds with albinism.
Melanosome:
- A pigmentgranule within the melanocyte and/or within the featherbarbules.
Microchromosome:
- A chromosome that is almost to small to positively identify as a chromosome.
- Therefore the exact number of chromosomes in the Budgerigar is higher than in most
- reference books.
Modifier:
- Secondary genes that modify the expressivity of a co-dominant or dominant gene.
Phaeomelanin:
- A reddish or foxbrown form of the pigment melanin which has never been
found in
- psittacine species.
Phenotype:
- The appearance. What the dominant genes express.
Pigment:
- A coloring matter. Pigment absorbs light in the medullas of the featherbarbules.
The eye
- sees the light that is not absorbed but reflected back.
Pleiotropism:
- The control by a single gene of several distinct and seemingly
- unrelated phenotypic effects.
Recessive:
- Referring to an altered gene which does not shows its effect if the bird carrying
that
- gene also has an unaltered gene.
Retina:
- The surface on the inside of the back of the eye. Light enters the eye through the
pupil,
- and the lens focuses the light on the retina. The retina converts the light to a message to
-
the brain.
Sex-linked:
- Any gene on the Z-chromosome.
Species:
- A set of creatures which, in their natural setting, breed among themselves.
Transposon:
- Segment of DNA that moves to a new location in a chromosome, or to another chromosome,
and alters the
- existing genetic instructions, sometimes producing significant changes.
- They are able to trigger changes in gene expression by shutting of genes or causing insertion mutations.
Tyrosine:
- An amino acid used by the system to make melanin.
Tyrosinase:
- An enzyme or specialized protein substance in the pigment cell which promotes
-
the conversion of the amino acid tyrosine to DOPA in the process of making pigment.
X-linked:
- Referred to a gene that is passed on with the Z-chromosome. Male birds have two
-
Z-chromosomes, while female birds have one Z-chromosome.
Inte Onsman
MUTAVI Research & Advice Group
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